Reinforcement of Friction Plug Welds

ABSTRACT

A hole in a metal workpiece is filled by friction plug welding. The weld between the workpiece and the plug is reinforced by a weld land in the workpiece that surrounds one end of the plug. The weld land is formed by extruding a portion of the plug into a cavity in an anvil used in the welding process.

TECHNICAL FIELD

This disclosure generally relates to welding processes, especiallyfriction and forge welding, and deals more particularly with a methodand apparatus for reinforcing friction plug welds.

BACKGROUND

Friction welding is a type of solid-state welding process that generatesheat through mechanical friction between a moving workpiece and astationary component in combination with a lateral force thatplastically displaces and fuses the materials. Friction welding may beused with a variety of metals and thermoplastics in a wide range ofapplications, including those in the aerospace, marine and automotiveindustries. Friction welding may be advantageous in some applicationscompared to other welding processes for a variety of reasons, includingthe ability to join dissimilar materials, relatively short joining timesand the ability to limit heat input to the weld interface.

In one application of friction welding, referred to as friction plugwelding, a tapered plug is friction welded into a tapered hole in asubstrate. This welding technique may be used to repair castings or tofill holes that occur on the completion of a friction stir welding passwhen a stirring probe is withdrawn from the weld.

The weld strength properties of friction plug welds along the line ofthe fusion may be less than desired in some applications. For example,when used to close a termination hole on a circumferential friction stirweld on a tank, the strength of the friction plug weld along its line offusion with the parent tank material may be less than the strength ofthe friction stir weld.

Accordingly, it would be desirable to provide a method and apparatus forfriction plug welding that exhibits improved weld strength properties.

SUMMARY

The disclosed embodiments provide a method and apparatus for makingfriction plug welds that include reinforcement. The reinforcement isformed by a weld land that surrounds the plug and increases the strengthof the plug weld. The additional strength provided by the weld land mayallow the weld to perform more consistently and with increased loadcarrying capability. Repairs made with the disclosed friction plugwelding method may be rated at higher strength capacities, and otherload bearing structures incorporating such welds may be designed tocarry greater loads. The disclosed embodiments may be used in a varietyof applications including, but not limited to, closing termination holesin friction stir welds, repairing parts such as castings, and attachingcomponents to structures. Higher weld strengths may be achieved withoutsubstantially increasing time and/or material cost. The disclosedembodiments may also be used in connection with building up varioustypes of blanks that may be formed into parts through forging, machiningor other processes.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

FIG. 1 is an illustration of a functional block diagram of apparatusused to make reinforced friction plug welds.

FIG. 2 is an illustration of a plan view of a circumferential frictionstir weld on a barrel section, including a termination hole closed witha friction plug weld.

FIG. 3 is an illustration of an isometric view of one side of aworkpiece having a friction plug weld, and showing a reinforcing weldland.

FIG. 4 is an illustration similar to FIG. 3 but showing the oppositeside of the workpiece.

FIG. 5 is an illustration of a simplified flow chart showing the stepsof a method of making reinforced friction plug welds.

FIG. 6 is an illustration of a cross sectional view of apparatus formaking reinforced friction plug welds, and showing the plug immediatelybefore insertion into the workpiece hole.

FIG. 7 is an illustration of a cross sectional view of an anvil formingpart of the apparatus shown in FIG. 6.

FIG. 8 is an illustration of the tip of the plug forming art of theapparatus shown in FIG. 6.

FIGS. 9-11 are cross sectional views of the apparatus shown in FIG. 6,respectively showing the progressive stages of making a friction plugweld.

FIG. 12 is an illustration of the area designated as “A” in FIG. 11.

FIG. 13 is an illustration of a side view showing excess portions of theplug being removed from the workpiece following welding.

FIG. 14 is an illustration similar to FIG. 12, but showing a modifiedform of the anvil having recess for forming a coin around the weld land.

FIG. 15 is an illustration of a plan view of the modified anvil shown inFIG. 14.

FIG. 16 is an illustration of a sectional view showing an alternate formof apparatus for making reinforced friction plug welds.

FIG. 17 is an illustration a side view showing a fully formed weld madeby the apparatus of FIG. 16, wherein excess portions of the plug arebeing removed.

FIG. 18 is an illustration of a plan view of a workpiece having a weldthat has been reworked using reinforced, overlapping friction plugwelds.

FIG. 19 is an illustration of a flow diagram of aircraft production andservice methodology.

FIG. 20 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIG. 1, apparatus generally indicated by the numeral20 may be used to carry out a method of making reinforced friction plugwelds. The disclosed method and apparatus 20 are particularly useful inmaking friction plug welds between metal materials such as aluminumalloys, however the welded parts may comprise other materials, such aswithout limitation, thermoplastics. A shaped plug 24 is spun about itslongitudinal axis 21, as shown by the arrow 28 as a force 30 is appliedto the plug 24 that forces the spinning plug 24 through a hole 26 in aworkpiece 22. Friction generated between the spinning plug 24 and theworkpiece 22 as the plug 24 is being forced through the hole 26 producesheat that plasticizes both the plug 24 and the workpiece 22 at theirfrictional interface 23 to produce a weld 33.

As the spinning plug 24 is forced through the hole 26, the plug 24engages and is forced against an anvil 32 that is configured to extrudethe plasticized plug 24 and the workpiece 22 in a manner that forms aweld land 34 in the workpiece 22 surrounding the plug 24 and the weld33. After the spinning plug 24 has been plunged through the hole 26 andagainst the anvil 32, the torque used to spin the plug 24 is removed,resulting in the plug 24 coming to a stop, however the force 30 may bemaintained for a short period, causing the plug 24 to be forge welded tothe workpiece 22. The weld land 34 functions to reinforce the resultingweld 33.

FIG. 2 illustrates a typical application in which a friction stir weld36 extends circumferentially around a cylindrical workpiece 22 andterminates in a hole 26 in the workpiece 22 caused by withdrawal of afriction stir weld probe (not shown). The apparatus shown in FIG. 1 maybe employed to close the hole 26 by friction plug welding, in which aweld plug 24 fills the hole 26 and is joined to the workpiece 22 by aweld 33 that is reinforced by a weld land 34 surrounding the weld 33.

FIGS. 3 and 4 illustrate a reinforced friction plug weld 33 madeaccording to the disclosed embodiments. A raised, ring shaped weld land34 having a width W₁ is formed in one side 22 a of the workpiece 22shown in FIG. 3 which surrounds one end 27 of the plug 24 and reinforcesa weld between the plug 24 and the workpiece 22. FIG. 3 illustrates theroot side 33 a of the weld 33, while FIG. 4 illustrates the face side ofthe weld 33. In FIGS. 3 and 4, the ends 27, 29 of the plug 24 have beencut off.

FIG. 5 broadly illustrates the basic steps of a method for forming areinforced friction plug weld 33 described generally above. Beginning atstep 40, the plug 24 is rotated about its axis 21 (FIG. 1) at a desiredspeed and a selected level of torque. The anvil 32 is placed against oneside 22 a of the workpiece 22, overlying and substantially aligned withthe workpiece hole 26, as shown in step 42. At 44, the rotating plug 24is forced through the workpiece hole 26 resulting in the interface 23between the plug 24 and the workpiece 22 becoming plasticized throughfrictional heat. As shown in 46, the plug 24 continues its displacementuntil it is forged against the anvil 32.

At step 48, the weld land 34 is formed on the root side 33 a of the weld33, surrounding one end 27 of the plug 24 as a result of the extrusionof the plasticized plug 24 and partial collapse of a portion of theworkpiece 22 into a later discussed countersink 32 c (FIG. 6) in theanvil 32. At step 50, rotation of the plug 24 is stopped while forgingforce 30 (FIG. 1) is maintained on the plug 24 for a period of timeuntil the weld 33 is complete. Finally, at step 51, the exposed portionsof the plug 24 extending beyond the workpiece 22 on both the root side33 a and the face side 33 b of the weld 33 the may be flush cut awayfrom the workpiece 22.

Attention is now directed to FIG. 6 which illustrates additional detailsof an embodiment of the apparatus 20 for forming a reinforced frictionplug weld. In this example, a cylindrical metal plug 24 made, as bymachining or casting to a desired diameter d, includes a lower taperedtip 24 a that is axially aligned with a hole in a workpeice 22. In theillustrated example, the workpiece hole 26 is shown as being taperedhowever, other cross sectional shapes are possible, including, withoutlimitation, a hole 26 having straight sides (not shown). The diameter dof the plug 24 is greater than the maximum diameter of the hole 26.

An anvil 32 has an upper face 35 adapted to engage one side 22 a of theworkpiece 22, in substantially face-to-face contact. The anvil 32includes a circular cavity 32 a having a central circular depression 32b for receiving the tip 24 a of the plug 24. The circular depression 32b is defined by lower inclined sidewalls 32 c and an upper, taperedcountersink 32 d formed by an inclined countersink wall 32 e. While thecountersink 32 d is shown as having a tapered profile due to theinclination of the countersink wall 32 e, other profiles are possible.Also, the cavity 32 a as well as the depression 32 b may have a shapeother than circular. The countersink wall 32 e extends radially outwardbeneath the workpiece 22, so that the workpiece 22 forms a ledge-likelip 22 d overhanging the countersink wall 32 e.

FIGS. 7 and 8 illustrate additional details of the anvil 32 and the plug24, respectively. The diameter D of the central cavity 32 a may bemarginally greater than the diameter d of the plug 24. The includedangle θ defining the inclination of the tapered countersink 32 d, i.e.the angle between opposite sides of the countersink wall 32 e, may varywidely, depending on the application, and may or may not besubstantially different than the included angle Φ₁ defining theinclination of the tapered tip 24 a of the plug 24. As will be discussedlater, higher values of θ result in a tapered countersink 32 d having agreater width W₂, which in turn produces a weld land 34 having a greaterwidth W₁ (FIG. 3). The included angle Φ₁ of the tapered tip 24 a of theplug 24 may be generally similar to the included angle Φ₂ of thesidewalls 32 c defining the depression 32 b. In some applications, arelatively large included angle θ may be desirable, irrespective of theincluded angle Φ₁ of the tapered tip 24 a of the plug 24. For example,and without limitation, in one practical embodiment, an included angle θof approximately 90 degrees was found to provide substantially optimalresults. A larger included angle θ increases the width W₂ of thecountersink 32 d, thereby increasing the cross sectional area of theweld land 34. A weld land 34 having a greater cross sectional area mayaid in reducing stress applied to the weld 33. Additionally, arelatively large included angle θ may shorten the amount of displacementof the plug 24 required to completely fill the anvil cavity 32 a, whichmay allow the weld 33 to be made with lower overall heat input, andtherefore possibly less degradation of material properties.

Referring again to FIG. 6, a friction plug weld is completed by theapparatus 20 in essentially two phases. The first phase begins at weldinitiation, and ends when cavity 32 a including the countersink 32 d hasbeen filled by the plug 24. During this first phase, the combination ofthe frictional heat generated by the engagement of the plug 24 with theworkpiece 22 and the downward force 30 applied to the plug 24 issufficient to plasticize the plug 24 so that it may be extruded into thecavity 32 a. The plug 24 continues to plunge into the cavity 32 a in theanvil 32 until the cavity 32 a including the countersink 32 d, aresubstantially completely filled. The second phase of making the weld 33starts when the cavity 32 a in the anvil 32 has been filled with theplug material 24 and ends when the weld 33 is complete.

FIGS. 9, 10 and 11 respectively show the progressive stages of making afriction plug weld 33 having a reinforcing weld land 34 using theapparatus 20. In FIG. 9, the tapered tip 24 a of the spinning plug 24 isforced down into the workpiece hole 26 and frictionally engages theworkpiece 22 around the hole 26, thereby heating and plasticizing boththe plug 24 and the workpiece 22 in the area of their frictionalinterface 23. Because the plug diameter d (FIG. 6) is greater than thatof the workpiece hole 26, the plug 24 forces the workpiece 22 tightlyagainst the anvil 32. The heat frictionally generated at the interface23 extends radially outwardly to include the surrounding lip 22 d on theworkpiece 22, thereby plasticizing the lip 22 d so that it may bedisplaced downward into the countersink 32 d and against the countersinkwall 32 e.

FIG. 10 shows the plug 24 having been displaced slightly further towardthe anvil 32, causing the plasticized lip 22 d to begin being displacedor folded over into the countersink 32 d, and particularly toward thecountersink wall 32 e. FIGS. 11 and 12 show the final displacement ofthe plug 24 in which the plug 24 has engaged the anvil 32 and hasdisplaced the workpiece lip 22 d into the cavity 32 a and pressed itagainst the countersink wall 32 e, thereby forming the weld land 34around the root side 33 a of the weld 33 (FIG. 12).

Referring to FIG. 13, upon completion of a weld, portions 24 b, 24 c ofthe plug 24 that extend beyond the workpiece 22 may be removed, as bysawing, grinding or other processes, leaving a weld land 34 having aheight h₁ which surrounds the welded plug 24.

Attention is now directed to FIGS. 14 and 15 which illustrate anotherembodiment of the apparatus 20 that is similar to that shown in FIGS.6-12, but wherein a ring shaped recess 32 f is formed in the anvil 32.The recess 32 e is contiguous with, and extends radially outward fromthe countersink wall 32 e. Although the recess 32 f is shown as having arectangular cross section in the illustrated embodiment with apreselected height h₂ and width W₃, other cross sectional shapes arepossible. The recess 32 f may be formed in the anvil 32 by machining orother process.

The recess 32 f allows a ring-shaped coin 39 to be formed on the rootside 33 a of the weld 33 that is effectively a relatively shallow radialextension of the weld land 34. Formation of the coin 39 begins duringphase one of the weld 33 discussed previously, and continues throughoutphase two. The plasticized material from the workpiece lip 22 d and/orthe plug 24, is displaced radially outward as the weld progresses, and aportion 37 (FIG. 14) of this material may be extruded into the recess 32f to form the coin 39. The width W₄ of the coin 39 increases asdisplacement of the plug 24 continues through phase two of the weld. Thefinal width W₄ of the coin 39 may be determined by the diameter d of theplug 24 and the amount of material from the workpiece 22 that isdisplaced by the plug 24. Larger diameters of the plug 24 result in awider coin 39. The height of the coin 39 is determined by the height h₂of the recess 32 f in the anvil 32. The coin 39 may add additionalstrength around the weld 33 which may reduce the amount of tensile loadstransmitted through the workpiece 22 to the weld 33.

Attention is now directed to FIGS. 16 and 17 which illustrate anotherform of the apparatus 20. In this example, the hole 64 in the workpiece22 is cylindrical and the plug 24 includes a shaft 60 that extendsthrough both the hole 64 and an opening 54 in the anvil 32. The lowerend 60 a of the shaft 60 is held in a chuck 62 that rotates, as shown bythe arrow 28, and is drawn axially downward by a force indicated by thearrow 30. The upper end of the plug 24 includes a tapered head 56including a cap 58. In this example, the chuck 62 rotates the plug 24while pulling it downwardly through the anvil 32 so that the taperedsides 56 a of the head 56 engage the workpiece 22 to create thenecessary frictional heat which plasticizes the head 56. As the head 56becomes plasticized, it is extruded downwardly through the workpiecehole 64 into the countersink 32 c where it solidifies to form the weldland 34, similar to the example previously described in connection withFIGS. 6-13. Following completion of the weld, as shown in FIG. 17, thecap 58 of the head 56, as well as the shaft 60 may be removed from theplug 24.

As previously discussed, the disclosed method and apparatus for formingreinforced friction plug welds may be employed in various applicationsincluding closing termination holes formed during friction stir weldingand to attach parts to structures. Also, as shown in FIG. 18, thedisclosed embodiments may be employed to rework an area of a weld 36which may not have desired performance standards. In this example, aseries of overlapping holes (not shown) are successively formed and thenclosed with plugs 24 using the disclosed friction plug welding method inwhich each of the welded plugs is surrounded by a weld and 34. Thereinforced friction plug welds may restore the area 66 of the weld 36 tothe desired performance standards.

Embodiments of the disclosure may find use in a variety of potentialapplications, particularly in the transportation industry, including forexample, aerospace, marine and automotive applications. Thus, referringnow to FIGS. 19 and 20, embodiments of the disclosure may be used in thecontext of an aircraft manufacturing and service method 70 as shown inFIG. 19 and an aircraft 72 as shown in FIG. 20. During pre-production,exemplary method 70 may include specification and design 74 of theaircraft 72 and material procurement 76 in which the disclosedreinforced friction plug welds may be specified for use in assemblingparts or components used in the aircraft 72. During production,component and subassembly manufacturing and system integration 80 of theaircraft 72 takes place. The disclosed method and apparatus may be usedto fasten or join parts during these production processes. Thereafter,the aircraft 72 may go through certification and delivery 82 in order tobe placed in service 84. While in service by a customer, the aircraft 72is scheduled for routine maintenance and service 86 (which may alsoinclude modification, reconfiguration, refurbishment, and so on). Thedisclosed method and apparatus may be used to repair parts or componentsduring the maintenance and service 86.

Each of the processes of method 70 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 20, the aircraft 72 produced by exemplary method 70 mayinclude an airframe 88 with a plurality of systems 90 and an interior92. The disclosed method and apparatus may be used to form reinforcedwelds on parts which form part of, or may be installed on the airframe88. Examples of high-level systems 90 include one or more of apropulsion system 94, an electrical system 96, a hydraulic system 98,and an environmental system 100. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosure may be applied to other industries, such as the marine andautomotive industries.

The disclosed method and apparatus may be employed to make welds duringany one or more of the stages of the production and service method 70.For example, components or subassemblies corresponding to productionprocess 78 may incorporate parts that are welded using the disclosedmethod and apparatus. Also, one or more method embodiments, or acombination thereof may be utilized during the production stages 78 and80, for example, by substantially expediting assembly of or reducing thecost of an aircraft 72. Similarly, the disclosed method and apparatusmay be used to weld parts that are utilized while the aircraft 72 is inservice.

Although the embodiments of this disclosure have been described withrespect to certain exemplary embodiments, it is to be understood thatthe specific embodiments are for purposes of illustration and notlimitation, as other variations will occur to those of skill in the art.

1. A method of filling a hole in a metal workpiece, comprising: frictionwelding a plug in the hole; and forming a weld land in the workpiecesubstantially surrounding the plug.
 2. The method of claim 1, whereinthe friction welding is performed by: rotating the plug, and forcing therotating plug into the hole.
 3. The method of claim 1, wherein formingthe weld land is performed by: plasticizing the plug, placing an anvilagainst the workpiece and around the hole, and extruding the plasticizedplug into a cavity within the anvil.
 4. The method of claim 3, whereinthe extruding is performed by extruding the plasticized plug radiallyoutwardly into the cavity.
 5. The method of claim 3, further comprising:forming a coin in the workpiece surrounding the weld land.
 6. The methodof claim 6, wherein forming the coin is performed by extruding a portionof the plasticized plug into a recess surrounding the cavity.
 7. Themethod of claim 1, further comprising: removing portions of the plugthat extend beyond the workpiece after the plug has been friction weldedin the hole.
 8. A method of friction plug welding a workpiece,comprising: rotating a metal plug; plasticizing the plug and filling ahole in the workpiece by forcing the rotating plug through the hole andagainst an anvil; and, forming a weld land on the workpiece around theplug.
 9. The method of claim 8, wherein forming the weld land includesextruding a portion of the plasticized plug into a cavity in the anvil.10. The method of claim 8, wherein forming a weld land includesdisplacing a portion of the workpiece into a countersink in the anvil.11. The method of claim 8, wherein forcing the rotating plug through thehole is performed by pulling the plug through the hole.
 12. The methodof claim 8, wherein forcing the rotating plug through the hole isperformed by pushing the plug through the hole.
 13. The method of claim8, further comprising: forming a coin in the workpiece around the weldland.
 14. The method of claim 13, wherein forming the coin includesextruding a portion of plug radially outward into a recess in anvil.15-19. (canceled)
 20. A method of friction plug welding a metalworkpiece, comprising: rotating a metal plug; forcing the rotating pluginto one end of a hole passing through the workpiece; plasticizing theplug using heat generated by frictional engagement between the rotatingplug and the workpiece; placing an anvil against the workpiece; forgewelding the plug to the workpiece, including forcing the plasticizedplug against the anvil; reinforcing the weld by extruding a portion ofthe plasticized plug into a cavity in the anvil to form a weld land onthe workpiece surrounding one end of the plug; and, forming a coin inthe workpiece around the weld land by extruding the plasticized pluginto a recess in the anvil.